The Internet has dramatically increased the potential for data, voice, and video services for customers. Existing circuit-switched telephony systems, however, do not provide the foundation to support the growing need for bandwidth and new services required by both residential and business consumers. As a result, integrated access devices (IADs) have been introduced to support Internet and related technologies as well as standard telephony service for customers.
IADs often combine synchronous and asynchronous transport and switch functionality to multiplex data, voice, and video traffic together onto a single network. Within an IAD, a time division multiplex (TDM) bus is typically used to transport voice and other synchronous traffic between the line cards and a switch core. An asynchronous transfer mode (ATM) bus is used to transport ATM traffic between the line cards and the switch core.
At the switch core, ATM traffic normally arrives asynchronously while TDM traffic arrives in a regular and periodic fashion. Separate ATM and TDM switch hardware are provided to receive and process the ATM and TDM traffic, respectively.
Typically, the TDM traffic is switched by a synchronous switch such as a time slot interchanger (TSI) that cross-connects the TDM channels based on switching instructions in a switching memory. The switching instructions are preprogrammed into the switching memory by a processor and may be altered by the processor in response to protection switching and other events.
For 1:N protection switching, a standby card in the system is provided to be activated in case one of a number of designated cards malfunctions. When a defect is detected in an operating card and the standby card is activated in its place, the switching memory for the TSI is reprogrammed to write each instruction for the failed card to the instructions for the activated card. This reprogramming of the switching memory involves a large number of microprocessor operations which are relatively time consuming. As a result, protection switching is slowed down in the TSI and may not conform to some telecommunication standards.